A semiconductor device includes a semiconductor substrate with an aluminum electrode thereon and a heat sink soldered on the aluminum electrode through a metallic electrode. This semiconductor device is disclosed in Japanese Patent Application Publications No. 2002-110893 and No. 2003-110064. In this device, a protection film is formed on the aluminum electrode disposed on one surface of the semiconductor substrate. Then, an opening is formed in the protection film so that the surface of the aluminum electrode is exposed from the opening. Next, a metallic electrode for soldering is formed on the surface of the aluminum electrode through the opening by a plating method or the like. In these processes, a bump electrode technique is used. The bump electrode technique is disclosed in Japanese Patent Application Publication No. S63-305532.
In general, adhesion between the aluminum electrode and the metallic electrode is comparatively weak. Therefore, the metallic electrode may be removed from the aluminum electrode.